Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 121830 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 230 PM EDT SAT APR 12 2014 .SYNOPSIS...
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A WARM FRONT WILL LIFT NORTHWARD ACROSS THE AREA TONIGHT. A COLD FRONT WILL GRADUALLY MOVE THROUGH THE REGION LATE MONDAY NIGHT INTO TUESDAY...WITH HIGH PRESSURE BUILDING INTO THE AREA FOR THE SECOND HALF OF THE WEEK.
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&& .NEAR TERM /THROUGH SUNDAY/...
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DRY AIR ALOFT HAS MIXED DOWN TO THE SFC THIS AFTERNOON...HELPING TEMPERATURES OVERACHIEVE A BIT AS DEWPOINTS HAVE DROPPED INTO THE 20S AND 30S. CONVECTIVE CU HAS DEVELOPED IN THE SW PORTIONS OF THE CWA WHERE SFC MOISTURE STILL EXISTS. THERE ARE NOT YET RADAR ECHOES IN THIS REGION...BUT HI-RES MODELS STILL INDICATE THE POTENTIAL FOR -SHRA DEVELOPMENT BETWEEN 22Z AND 02Z...AND THIS CONTINUES TO BE REFLECTED IN THE GRIDS. TONIGHT...SFC MOISTURE WILL BE ON THE INCREASE AS A WARM FRONT MOVES NORTHWARD AND LOW-LEVEL MOISTURE SURGES. MODELS HAVE BACKED OFF THE DEEP LOW-LEVEL MOISTURE SOMEWHAT...BUT STILL APPEARS THERE WILL BE SOME POTENTIAL FOR STRATUS DEVELOPMENT...PATCHY FOG...OR BOTH. HAVE REFLECTED THESE IN THE GRIDS AND TAFS OVERNIGHT. GIVEN THE POTENTIAL FOR CLOUD COVER AND WINDS STAYING UP...HAVE GONE A BIT ABOVE GUIDANCE...BUT NOT AS HIGH AS I MIGHT HAVE GIVEN THE CURRENTLY LOW DEWPOINTS. SUNDAY APPEARS TO BE A FANTASTIC...IF NOT SOMEWHAT HUMID...DAY. EARLY STRATUS WILL GIVE WAY TO SCATTERED DIURNAL CUMULUS CLOUDS. THE DEEP SOUTHERLY FLOW WILL YIELD HIGHS AROUND 80...BUT WITH DEWPOINTS IN THE MIDDLE IF NOT UPPER 50S. WINDS WILL BE GUSTY IN THE AFTERNOON...WITH WIND GUSTS NEAR 30 MPH POSSIBLE.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
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SOUTHERLY FLOW PERSISTS SUNDAY NIGHT. SOME LOW CLOUD DEVELOPMENT IS POSSIBLE BUT DECOUPLING WILL NOT OCCUR. GIVEN PERSISTENT LOW-LEVEL MOISTURE AND THE WIND...LOWS MAY HAVE A DIFFICULT TIME DROPPING MUCH BELOW 60 EAST OF THE BLUE RIDGE. DEEPER MOISTURE APPROACHES BY LATE MONDAY AS A COLD FRONT ORGANIZES SLOWLY PUSHES ACROSS THE EASTERN GREAT LAKES AND OHIO VALLEY. WHILE I AM NOT PARTICULARLY CONVINCED ABOUT CONVECTIVE POTENTIAL WELL AHEAD OF THE FRONT ON MONDAY...AS THE DEEPER MOISTURE ARRIVES LATE IN THE DAY...COMBINED WITH SOME TERRAIN LIFT...MOUNTAIN -SHRA WILL BE POSSIBLE...MAYBE EVEN A TSTM. CLOUDS SPREADING NORTHWARD AHEAD OF THE SYSTEM WILL HOLD HIGHS DOWN JUST A BIT COMPARED TO SUNDAY...BUT STILL WELL ABOVE NORMAL. PRECIPITATION SPREADS FURTHER EAST MONDAY NIGHT AS THE FRONT APPROACHES. STILL SOME UNCERTAINTY WHETHER THERE WILL EVEN BE MUCH PRE-FRONTAL PRECIP...SO POPS WERE KEPT BELOW CATEGORICAL ON MONDAY NIGHT IN ALMOST ALL AREAS. A TSTM CANNOT BE RULED OUT AT ANY TIME DURING THE NIGHT. THE BEST CHANCE OF RAIN APPEARS TO BE TUESDAY MORNING /THOUGH THAT TIMING IS NOT YET A LOCK/ AS THE FRONT PUSHES THROUGH. RAIN COULD BE HEAVY TUESDAY MORNING WITH PWATS AROUND 1.5 INCHES...BUT THE SYSTEM IS PROGRESSIVE OVERALL...WHICH WILL LIMIT A FLOOD THREAT. AVERAGE RAINFALL LOOKS TO BE AROUND AN INCH.
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&& .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
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A STRONG PUSH OF COLD AIR...WITH 850 MB TEMPERATURES AT OR BELOW 0 C WILL MOVE INTO THE REGION BEHIND A DEPARTING COLD FRONT TUESDAY EVENING. SNOW SHOWERS COULD MIX WITH ANY LINGERING PRECIPITATION GENERALLY AT ELEVATIONS AT OR ABOVE 1500 FEET. LOW TEMPERATURES WILL BE WELL BELOW NORMAL...GENERALLY IN THE 30S AREA-WIDE. A WAVE OF LOW PRESSURE WILL DEVELOP ALONG THE FRONT AND MOVE NORTH ALONG THE EASTERN SEABOARD DURING THE DAY WEDNESDAY. MODELS/ENSEMBLES DIFFER ON HOW FAR EAST THE FRONT GETS BY THE TIME LOW PRESSURE APPROACHES FROM THE SOUTH. THE 00Z DETERMINISTIC ECMWF IS SLOWEST AND FURTHEST WEST WITH THE FRONT AND WAVE OF LOW PRESSURE...WITH THE 12Z GFS FURTHER EAST. FOR NOW HAVE CHANCE POPS ACROSS THE VA PIEDMONT AND I-95 CORRIDOR ON EAST WHERE HIGHEST CHANCE OF RAIN WOULD BE. HIGH PRESSURE WILL MOVE ACROSS THE AREA WEDNESDAY NIGHT THROUGH THURSDAY WITH DRY WEATHER AND BELOW NORMAL TEMPERATURES EXPECTED. ANOTHER STORM SYSTEM MAY APPROACH THE AREA TOWARDS THE END OF NEXT WEEK...BUT TRACK AND TIMING DETAILS ARE FAR FROM CERTAIN AT THIS JUNCTURE.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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THERE IS SOME POTENTIAL FOR LOW STRATUS AND/OR PATCHY FOG TONIGHT. BOTH ARE HINTED AT IN THE TAFS WITH MVFR CIGS/VSBY BUT DID NOT GO LOWER THAN THAT FOR EITHER AT THIS TIME. OTHERWISE...VFR EXPECTED THROUGH SUNDAY. WINDS WILL BECOME GUSTY BY SUNDAY AFTERNOON...AND REMAIN FAIRLY BREEZY/GUSTY THROUGH TUESDAY. LOWER CIGS/VSBY POSSIBLE IN -SHRA MONDAY NIGHT AND TUESDAY. TSRA ARE POSSIBLE AS WELL. SUB-VFR STILL POSSIBLE IN SHOWERS TUESDAY NIGHT...POSSIBLY PERSISTING INTO WEDNESDAY ESPECIALLY FOR SOUTHERN AND EASTERN TERMINALS /I.E. BWI-DCA-CHO SOUTH AND EAST/. NORTHERLY FLOW AROUND 10 KNOTS.
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&& .MARINE...
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GENERALLY LIGHT WINDS OVERNIGHT. SOUTHERLY FLOW INCREASES ON SUNDAY...AND A SMALL CRAFT ADVISORY IS IN EFFECT. THAT ADVISORY HAS BEEN EXTENDED THROUGH SUNDAY NIGHT...AND LIKELY WILL HAVE TO BE EXTENDED BEYOND THAT THROUGH THE FIRST PART OF NEXT WEEK AS THE SOUTHERLY FLOW PERSISTS. GUSTY NORTHERLY FLOW BEHIND DEPARTING COLD FRONT/WAVE OF LOW PRESSURE COULD RESULT IN SCA LEVEL GUSTS ON PARTS OF THE WATERS WEDNESDAY. HIGH PRESSURE NEAR THE AREA SHOULD THEN PRECLUDE SCA CONDITIONS THROUGH THURSDAY.
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&& .TIDES/COASTAL FLOODING...
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TIDAL ANOMALIES ARE CURRENTLY BETWEEN 0.5 AND 1.0 FOOT BELOW NORMAL...BUT AS SOUTHERLY FLOW COMMENCES...THE ANOMALIES WILL GRADUALLY TURN POSITIVE. WITH THE SOUTHERLY FLOW EXPECTED TO PERSIST THROUGH MONDAY NIGHT...WATER LEVELS COULD APPROACH MINOR FLOOD CRITERIA AT THE MORE SENSITIVE LOCATIONS BY MONDAY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM NOON SUNDAY TO 6 AM EDT MONDAY FOR ANZ530>543.
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&& $$ SYNOPSIS...JE NEAR TERM...JE SHORT TERM...JE LONG TERM...DFH AVIATION...JE/DFH MARINE...JE/DFH TIDES/COASTAL FLOODING...JE

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